An electron lens is classified into an electromagnetic type and an electrostatic type. The electrostatic type has a simple configuration compared to the electromagnetic type and is advantageous in miniaturization and high integration. As an electrostatic lens used in an electron beam exposure device, for example, an einzel lens shown in Non Patent Literature 1 is generally used. Of three electrode substrates constituting the einzel lens, two electrode substrates at both upper and lower ends are generally supplied with an earth potential, and an intermediate electrode substrate is supplied with a negative or positive potential. Each electrode substrate has a circular opening, and the einzel lens generates a converging effect to an electron beam passing through the opening.
Although the electrostatic lens is easier to produce compared to a magnetic lens, the sensitivity of an optical aberration with respect to a production error of a lens opening is high. In particular, astigmatism is sensitive to the circularity of an opening. When the circularity is degraded, the electron beam converged by the electrostatic lens exhibits astigmatism or other high-order aberrations. An example of a method of forming an opening having a desired shape is photolithography. Patent Literature 1 discloses a method in which a light-curable resin film is formed on a plate with a nozzle hole formed therein, and the surface of the plate on which the light-curable resin film is not formed is exposed to light to fill the nozzle hole with the light-curable resin film. Then, according to this method, a plated layer containing water-repellent particles is formed from the principal plane of the plate having the nozzle hole filled with the light-curable resin film, and the light-curable resin film is removed to form a hole in the plated layer. Thus, the hole of the plated layer is similar in shape to the nozzle hole, and can be set to have an equal size of or to be larger than the nozzle hole. In this method, the light-curable resin film formed by photolithography is used as a mold, and hence the hole reflecting the shape of the light-curable resin film is formed in the plated layer.